The objective of the proposed study is to develop a endovascular diode-laser based technique at a new wavelength for photothermal coagulation and destruction of the greater saphenous vein (GSV) for treatment of varicose veins. Varicose veins are a significant medical and cosmetic problem with high incidence, especially among women. The cause of varicose veins is reflux and pooling of blood due to incompetent venous valves. Traditional surgical methods have several limitations and endovascular RF and laser treatments are being increasingly used. The current endovascular treatments are highly effective but have certain limitations such as ease of use and unintended side effects of bruising and tenderness. The proposed treatment method with the new wavelength laser is expected to overcome these limitations. Specific aims of the study include: 1. Building a CW fiber coupled laser system, 2. Building a fiber delivery system with an automated constant speed pullback, 3. Demonstrating full thickness vein wall damage in an ex vivo porcine vein model, and 4. Optimizing the treatment parameters for maximal efficacy and minimal side effects. Successful completion of Phase I research will lead to an SBIR phase II proposal emphasizing the development of a commercially oriented laser system for treatment of varicose veins.